This invention relates to grease lubricating assemblies, and more particularly to a grease lubricating assembly for metering a constant supply of grease to a lubrication site, such as a bearing assembly or the like, under pressure condition to minimize separation of the grease into its components.
Grease lubrication assemblies can generally be divided into two groups, the manual types in existance from the time of Liebing's patented unit in 1893, up to and including refined versions at the advent of World War II, and the post war type which are characterized by two important features, i.e. reservoir visibility and some form of automatic grease metering or flow control. Examples of such latter types are described in U.S. Pat. Nos. 3,498,413 and 4,018,305 to Krieger and Tietje, respectively.
The grease lubricating assemblies of both the Kreiger and Tietje references have transparent cups for grease level visibility, are operated by a compression spring and have a metering system for controlling the rate of grease flow. The Tietje assembly was an improvement over the Kreiger assembly in that operation was based on a different metering principle and was generally considered to do a more effective job over a wider range of greases and environmental factors.
Both of such grease lubricating assemblies, however, exhibited many shortcomings. For example, the ratio of grease volume to overall assembly volume was too low for efficient space utilization. The assemblies required different strength compression springs for different weight greases. All such assemblies placed excessive forces, i.e. a force higher than necessary on the contained grease to thereby result in "oil-separation."
Such unit metering lubricating grease assemblies were provided with a spring having a spring force necessary to expel the grease from the reservoir. Since the minimum spring force must be maintained throughout the entire delivery cycle (from full to empty) the spring must, of necessity, be chosen which is still able to deliver such necessary force in an extended position (empty). This means that the spring will deliver approximately twice the required force in a compressed position (full). Of course, the variation in flow rate caused by the difference in spring force is essentially converted into a constant flow rate by the metering mechanisms, e.g. variable restriction type, built into such assemblies.
While solving the flow rate problem, the problem of such assemblies were the excessive force acting on the contained grease in the compressed mode (full). Grease is basically oil suspended in a matrix of additives which impart a variety of charateristics such as film retention, temperature range stability, extension resistance, etc. Industry has strived over the years to improve such grease qualities. One of the most important characteristics, however, is the ability to resist "oil-separation." Oil separation is caused by pressure over a period of time. The rate of separation caused by a given level of pressure may be increased or decreased by temperature changes, but, sustained pressure is deleterious. Therefore, any sustained pressure caused by spring force beyond the level required to move the grease to the bearing is excessive and undesirable, and increases the tendency of "oil-separation."